🔍 Key Concepts

• Twist locks vs. lashings – what each does in securing container stacks • How stack height affects stability and racking forces on containers • Standard practice for when additional securing (lashings) supplements twist locks under normal conditions

💭 Think About

• Think about why twist locks alone might be acceptable up to a certain tier, but not beyond it. • Consider how the forces on the bottom containers increase as you add more tiers on top. • Ask yourself: At what stack height do most container-securing manuals introduce lashing rods or wires in addition to twist locks?

✅ Before You Answer

• Verify how many tiers can normally be secured with twist locks only in good weather and sea conditions. • Check when standard lashing plans say "additional lashings required above this tier". • Make sure you distinguish normal conditions from heavy weather or special cargo where lashings might be used earlier.